A method for constructing a digital image of a three-dimensional surface of a physical object includes choosing a surface on the object and placing a projector equipped with a light source to face the object, and providing a mask defining a speckle pattern having a multitude of points with predetermined light intensities and/or colors. The optical axis of the projector is directed towards the surface to be imaged. The speckle pattern is projected, along the optical axis, onto the surface. A two-dimensional image of the speckle pattern is acquired and stored and deformed by an optical sensor disposed in the optical axis. The image of the deformed speckle pattern is compared with an image of the non-deformed speckle pattern, and then, for each point of the selection, at least the depth coordinate is calculated.